The invention relates to a method for operating an internal combustion engine with fuel injection, including a cylinder with a cylinder head and a piston disposed in the cylinder into which air and a first fuel quantity are fed to form a homogeneous base mixtureture for ignition and combustion in the engine together with a direct injection mixtureture.
In direct-injection internal combustion engines with compression ignition, homogenous lean fuel/air mixturetures are often brought to compression ignition, so that high efficiencies and improved exhaust emissions are achieved. In internal combustion engines of this type, the compression ignition results in steep pressure rises in the combustion chamber at high loads, which can have an adverse effect on operation.
DE 199 27 479 C2 discloses a method for operating an internal combustion engine operated with gasoline, in which the fuel/air mixture is subjected to spark ignition or compression ignition depending on the load point. In this case, a suitable, high compression ratio is provided for the compression ignition. In a part-load range of the internal combustion engine, the homogenous fuel/air mixtureture is compression-ignited, while in a full-load range and during a cold start of the internal combustion engine the fuel/air mixture is spark-ignited.
DE 198 04 983 A1 discloses a method for operating an internal combustion engine operating in accordance with the four-stroke principle, in which a homogenous lean base mixture of air and fuel is ignited by compression ignition. In this case, the fuel is introduced directly into the combustion chamber by direct fuel injection, in such a manner that, with the formation of a homogenous mixture, the input of energy resulting from the compression provides for a homogenous ignition, resulting in an extensive, self-accelerating release of energy. In this method, the combustion is optimized by varying the compression and by using a targeted final homogeneity of the fuel/air mixture.
According to the current state of the art, the combustion described above can only be controlled with difficulty, since the instant of compression ignition is dependent to a very considerable extent on the engine parameters and the environmental conditions. Therefore, it is attempted to control the initiation of the compression ignition with the aid of certain control variables, e.g. by means of a cylinder pressure signal. However, concepts of this type entail a high level of outlay on engine control technology, which increases the costs of producing internal combustion engines of this type.
Therefore, it is the object of the present invention to provide a method for operating an internal combustion engine in which the initiation of compression ignition is easy to control and reliable engine operation is ensured.